P0401

DTC P0401

CIRCUIT DESCRIPTION
The engine control module (ECM) performs a flow test on the exhaust gas recirculation (EGR) system during deceleration. The ECM does this by momentarily commanding the EGR valve to open while monitoring the signal of the manifold absolute pressure (MAP) sensor and the EGR position sensor. If the MAP signal is incorrect for the EGR pintle position, the ECM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow tests required to exceed the fail threshold may vary according to the amount of detected EGR flow error. If the ECM detects an EGR flow error, DTC P0401 sets.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

CONDITIONS FOR RUNNING THE DTC
- DTCs P0106, P0107, P0108, P0112, P0113, P0115, P0117, P0118, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0217, P0351, P0352, P0402, P0404, P0405, P0406, P0441, P0488, P0502, P0506, and P0507 are not set.
- The EGR flow test is performed once per ignition cycle.
- DTC P0401 runs multiple times on the first ignition cycle after the DTC is cleared from the ECM memory.
- The EGR flow test is ran in decel fuel cut-off (DFCO) mode with the following conditions present before deceleration occurs:
- The A/C compressor clutch does not change state during deceleration.
- The ambient air temperature is more than 3°C (37°F).
- The engine speed is between 1,550-2,900 RPM for automatic transmission or 1400-2,900 RPM for manual transmission before deceleration.
- The manifold absolute pressure (MAP) is between 10.3-37 kPa.
- The barometric pressure (BARO) is more than 72 kPa.
- The vehicle speed is more than 18 km/h (11 mph) before deceleration.
- The EGR flow test is ran when the following conditions are met during DFCO mode:
- The throttle position is less than 1 percent.
- The EGR position is less than 1 percent.
- The MAP does not vary more than 1 kPa.
- DTC P0401 runs continuously once the above conditions are met.

The vehicle speed needs to be more than 18 km/h (11 mph), and then allowed to decelerate. When the vehicle is decelerating, while meeting all of the criteria listed above, the ECM will enable the EGR flow test. As the EGR flow test is running, you will see the desired EGR Position parameter and the EGR Position Sensor parameter on the scan tool momentarily change from 0 to a calibrated value above 0. The EGR flow test will be disabled if one of the following conditions occur:
- The vehicle speed drops more than 4 km/h (3 mph).
- The engine speed increases more than 50 RPM during a decel.
- The actual EGR position is less than 90 percent of the commanded state.

CONDITIONS FOR SETTING THE DTC
The MAP changes monitored by the ECM during the EGR flow tests indicate an insufficient amount of EGR flow.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

TEST DESCRIPTION

Steps 1-3:

Steps 4-6:

Steps 7-10:

The numbers below refer to the step numbers on the diagnostic table.
3. MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.
7. An engine mechanical condition may cause the engine to operate poorly, which could cause a low vacuum condition.